1. Technical Field
The present disclosure refers to a control apparatus for LED diodes.
2. Description of the Related Art
Control devices for LED diodes are known in the art. Some of these devices include a dimmer. The dimmers are known in the art for regulating the light intensity of a light load, for example an incandescent bulb. As shown in FIG. 1, a known circuit for control a light load comprises a dimmer 1 electrically connected in series between an electrical load 2 and the power source 3, for example an AC household current. Dimming is obtained by adjusting the conduction angle of the dimmer 1 so that the RMS voltage across the load 2 varies with the adjustment of the conduction angle.
A dimmer comprising a TRIAC device is commonly known in the art. The last has generally a first main terminal, a second main terminal and a gate terminal. The TRIAC exhibits the following characteristics:
Bidirectional conduction through the main terminals, allowing AC to pass through;
The TRIAC is turned in and conduction is present between the main terminals when there is a trigger current present between gate terminal and the second main terminal;
Once triggered, the TRIAC remains on until a zero crossing of the AC power line at which point the device turns off and awaits the next trigger pulse or zero crossing of the AC power line. This characteristic allows phase angle control to be obtained.
Also the TRIAC does not remain in the on state after triggering without a current higher than the hold current passing through the main terminals; therefore the TRIAC has difficulty remain on when a low current is drawn through the main terminals, such as in the case of LED lighting.
At lower current levels, once the dimmer conducts, the load current does not satisfy the hold current requirement of the TRIAC and the dimmer enters a retriggering state that causes flickering of the LED light.
Moreover dimmable LED lighting uses an electronic AC to DC converter to operate, preferably a switching mode power supply that converts the AC input voltage to low voltage and high current to drive the LED diodes.
The dimmer has a low bias current as its power supply and the LED lighting load as to provide such low current; the electronic converter instead has a very low current consumption. This prevents the dimmer circuit from firing properly again causing ringing.
FIG. 2 is a lighting apparatus that includes a control circuit 4 for controlling LED diodes and a dimmer 1 according to prior art.